This invention relates to a process for producing thermoset resin impregnated fiber reinforced composite articles with a predetermined ammount of resin in order to produce a uniformly resin impregnated structure substantially free of air voids and free of vacuum induced monomer vapour bubbles. The process of vacuum bagging fiber reinforced composites is not new. Traditional methods have relied or, prewetting the fiber reinforcement with catalysed resin and then applying a peel ply or perforated release sheet to the resin impregnated reinforcement to define the inside surface of the article. An absorptive layer was then applied to the peel ply followed by an impervious sheet made from polyvinyl alcohol film or polyethylene film which was sealed to the mold periphery by a suitable tape such as butyl tape to form a sealed envelope. The impervious sheet was then fitted with one or more vacuum connections and a vacuum was applied. This resulted in any excess resin in the resin impregnated fiber composite being drawn through the peel ply and absorbed in the material lying between the peel ply and the impervious sheet. After curing, the impervious sheet with the adhesive was removed, then the absorptive layer and peel ply were removed. All of this was discarded as waste.
In recent years this process was modified. The fiber reinforcement was placed in the mold cavity in it's dry state. The peel ply was next applied followed by a distribution medium or spacer to hold the impervious outer sheet apart from the peel ply. The impervious outer sheet containing fittings for vacuum introduction and/or resin introduction to the distribution medium was applied last and sealed to the mold periphery by conventional sealing tape to form a sealed envelope. A vacuum was applied to the distribution medium and fiber reinforcement via the vacuum fittings or peripheral vacuum channels and the resin was introduced through the fitting(s) in the impervious outer sheet into the distribution medium. The resin was continuously drawn out via the vacuum passages and reintroduced to the resin inlet(s) or discarded until the fiber reinforcement was completely impregnated by the resin. After curing, the peel ply, distribution medium containing cured resin, impervious outer sheet and connecting hoses were discarded. Seemann's Pat. Nos. 4,902,215 and 5,052,906 discribe such a process as do Palmer (U.S. Pat. No. 4,942,013) and Fourcher (U.S. Pat. No. 4,312,819).
These current processes all use single use disposible apparatus to achieve the manufacture of a single article. The control of the manufacturing process with these techniques is very labour intensive and wasteful resulting in poor manufacturing economy. Most fiber reinforced composites use unsaturated polyesters, vinyl esters or epoxies. Unsaturated polyesters and vinyl esters are preferred because of their economy and handling characteristics. These resin systems contain reactive monomers such as styrene as a diluent and for cross linking of the polymer. Monomers such as styrene will boil at reduced atmospheric pressure resulting in the formation of vapour bubbles throughout the resin. This is a common problem when impregnating fiber reinforcements with these vacuum processes since the resin is continually exposed to vacuum until it cures.
Silicones have been used as mold making materials for many decades. Mold making silicones are expensive, generally platinum cured, two component systems that are widely available through all current silicone manufacturers. Herbert, in U.S. Pat. No. 5,087,193 refers to the use of such a silicone in conjunction with multiple layers of 10 oz. glass cloth as a reinforcing material to produce a flexible mold with a thickness of 3/8' to 5/8'. This type of structure poses two problems: The glass reinforcement is not compatable with the elongation characteristics of silicone and will delaminate on repeated flexing, and the thickness of the silicone mold will trap styrene vapour which will subsequently polymerize in the silicone and destroy the flexibility and release properties of the silicone.
Seemann's U.S. Pat. No. 5,316,462 also refers to the use of a similar silicone, Dow Corning Tooling Elastomer -THT for the manufacture of a bag with integral distribution channel network. Seemann mentions the use of unwoven nylon fibers to reinforce the silicone bag if necessary. The thickness of the Seemann bag necessitated by the integral resin channels creates the same problem of internal styrene polymerization and the complexity of the design is prone to tear propagation during removal of cured resin waste and handling, resulting in short bag life. The Seemann silicone bag does nothing to eliminate the excess resin waste or need for a discardable peel ply.